CN101124265B - Aromatic polyamide porous film, process for producing the same and secondary battery - Google Patents

Abstract

An aromatic polyamide porous film that excels in thin-film forming capability and can easily express stable porous characteristics even after use at high temperature for a prolonged period of time. There is provided an aromatic polyamide porous film consisting of a porous film composed mainly of an aromatic polyamide, characterized in that on at least one major surface thereof, when the range of section area S [mu]m<2> is measured by means of an atomic force microscope, the section area at a depth of 10 nm from the top surface, S(10) [mu]m<2>, and the section area at a depth of 20 nm from thetop surface, S(20) [mu]m<2>, simultaneously satisfy the relationships: 0.01=S(10)/S=0.3, and 5=S(20)/S(10)=20.

Description

Aromatic polyamide porous film, method for producing same, and secondary battery

technical field

The present invention relates to a porous aromatic polyamide film that can be suitably used for filters, separation membranes, battery separators, printed circuit boards, and the like.

Background technique

Various organic electrolyte solution secondary batteries are known as batteries capable of achieving high capacity, high voltage, and high energy density. In this organic electrolyte secondary battery (for example, a lithium ion battery), a porous polymer film capable of passing ions between the two electrodes is provided as a separator in addition to the electrolyte between the positive electrode and the negative electrode arranged oppositely.

In an organic electrolyte secondary battery such as a lithium ion battery, the presence of an unstable metal in the battery sometimes causes a short circuit, ignition, or the like. In particular, since molten metallic lithium is highly reactive, it is necessary to interrupt the circuit before the temperature in the battery reaches the melting point of lithium (=186° C.) in order to ensure safety. At present, as a countermeasure against this, it is known to use a porous polyethylene film or polypropylene film with a thickness of about 25 μm and a thickness lower than the melting point of lithium as a separator in the battery, so that it has the following functions (blocking ( Shut down) characteristics), that is, the function of melting the separator before melting the lithium, collapsing the pores, and forming an insulator. For example, Japanese Patent Application Laid-Open No. 3-203160 discloses that a polyethylene film exhibits the above-mentioned barrier properties at a temperature lower than the melting point of lithium, and proposes an explosion-proof secondary battery using the film.

However, the polyethylene film or polypropylene film used as such a separator not only has poor heat resistance, but also has limited thinning while maintaining the necessary strength. Considering the limited battery size, there is a problem that it cannot be expected to greatly improve the storage capacity. Ability issue. That is, if such a thin film is simply thinned, there may be a part with insufficient local strength or a part with insufficient shape retention as a separator at high temperature, which may cause troubles such as ignition in the battery. There is a fear that a separator having the desired ion permeability cannot be formed, so it cannot be made thinner than a certain level.

On the other hand, in recent years, as described in JP-A-8-111238, an electrolytic solution having substantially no ignition point has been proposed. Using such an electrolytic solution greatly improves the safety against fire and the like, so as long as the desired ion permeability is satisfied, it is possible to reduce the thickness of the separator.

In addition, as organic electrolyte secondary batteries, further reduction in size, higher capacity, higher voltage, etc. have been demanded even at the same size, and further thinning of separators used in these secondary batteries has been demanded.

Furthermore, when used as a separator for a secondary battery of an electric hybrid vehicle or a fuel cell vehicle, the temperature in the engine room becomes high during operation, and in order to obtain high output characteristics, it is advantageous to use the battery at a high temperature, so as Separators used in these batteries require higher heat resistance.

In such applications, it is preferable to use a porous film obtained by using a highly heat-resistant aromatic polyamide that has high rigidity, can be thinned, and does not substantially have a melting point (referred to as "aromatic polyamide porous film"). . Regarding the aromatic polyamide porous film, for example, JP-A-59-14494, JP-A-59-36939, JP-A-2001-98106, US Patent No. 6642282, JP-A-2002-30176 The gazette discloses the production method.

In addition, the porous film is disclosed in Japanese Patent No. 2615976 and Japanese Patent Application Laid-Open No. 2002-293979, and an example of the application of an aromatic polyamide porous film to a battery separator is disclosed in Japanese Patent Laid-Open No. 11-250890 Publication, JP-A No. 2002-42767 and JP-A No. 2001-43842 have been disclosed. That is, Japanese Patent No. 2615976 and Japanese Patent Application No. 2002-293979 disclose the invention of controlling the coefficient of expansion to reduce changes in response to temperature and humidity; The invention described in discloses the control of pore size and porosity to obtain the necessary ion permeability; the invention described in JP-A-2001-43842 discloses the purpose of improving the oxidation resistance of the positive electrode by forming an inorganic thin film on the surface.

However, when the above-mentioned porous aromatic polyamide film is used for a long time at high temperature such as in the engine room of an electric hybrid car, higher positive electrode oxidation resistance is required, and furthermore, it is easy to cause damage due to the precipitation of metal lithium. The clogging of the pores cannot therefore be said to be necessarily sufficient.

Contents of the invention

Therefore, the object of the present invention is to provide a method that does not require special secondary processing (such as coating of inorganic substances such as silicon) on the surface by strictly controlling the pore structure near the surface layer of the aromatic polyamide porous film. The battery separator can maintain stable battery characteristics even when it is used at a high temperature for a long period of time, and when the aromatic polyamide porous film is used as the battery separator, the surface is less likely to be oxidized and deteriorated on the positive electrode side (resistant to Porous aromatic polyamide film with high positive electrode oxidation property.

The present invention for achieving the above object is an aromatic polyamide porous film, which is characterized in that it contains aromatic polyamide, and at least one surface is measured at a depth of 10 nm from the surface when the range of S ^μm is measured using an atomic force microscope. The cross-sectional area S(10) μm ^{2 of} and the cross-sectional area S(20) μm ² at a depth of 20 nm from the surface simultaneously satisfy the following formula.

0.01≤S(10)/S≤0.3

5≤S(20)/S(10)≤20

In addition, according to the present invention, by using a highly rigid porous aromatic polyamide film that can be thinned as a battery separator, the capacity of each battery can be increased, and the heat resistance of the aromatic polyamide and its performance as a The characteristic pore structure near the surface of the present invention can achieve high output and maintain stable battery characteristics even in the case of long-term use at high temperatures, and when the aromatic polyamide porous film is used as In the case of a battery separator, a porous aromatic polyamide film whose surface is less prone to oxidative deterioration on the positive electrode side (high resistance to positive electrode oxidation) can be obtained.

Description of drawings

FIG. 1 is a diagram showing a cross section of a 3-dimensional network structure which is a characteristic structure of the present invention.

Fig. 2 is a diagram showing a section of a pore structure not within the scope of the present invention.

Fig. 3 is a diagram showing a section of a pore structure not within the scope of the present invention.

Fig. 4 is a diagram showing a cross-section of other pore structures not within the scope of the present invention.

Explanation of symbols

1: Solid component containing aromatic polyamide polymer

2: porosity

Detailed ways

Here, as the aromatic polyamide, an aromatic polyamide having a repeating unit represented by, for example, the following formula (1) and/or formula (2) is preferable.

Formula 1):

Formula (2):

Here, examples of Ar ₁ , Ar ₂ , and Ar ₃ groups include

etc., the groups of X and Y are selected from -O-, -CH ₂ -, -CO-, -CO ₂ -, -S-, -SO ₂ -, -C(CH ₃ ) ₂ -, etc., but not limited to These.

Furthermore, some of the hydrogen atoms on these aromatic rings are replaced by halogen groups such as fluorine, bromine and chlorine (especially chlorine), nitro, methyl, ethyl, propyl and other alkyl groups (especially methyl), methyl, etc. Compounds substituted with substituents such as alkoxy groups such as oxy, ethoxy, and propoxy are preferable because the hygroscopicity decreases and the dimensional change due to humidity changes becomes small. In addition, the hydrogens in the amide bond constituting the polymer may be substituted with other substituents.

In the aromatic polyamide used in the present invention, the portion having the above-mentioned para-orientation of the aromatic rings preferably accounts for 80 mol% or more of all aromatic rings, more preferably 90 mol% or more. The para-orientation referred to here refers to a state in which the divalent bonds constituting the main chain on the aromatic ring are coaxial or parallel to each other. When this para-orientation is less than 80 mol%, rigidity and heat resistance of a film may become inadequate. Furthermore, when the aromatic polyamide contains 60 mol% or more of the repeating unit represented by the formula (3), it is particularly excellent in stretchability and film properties, and therefore it is preferable.

Formula (3):

(here, p and q are integers from 0 to 4)

The aromatic polyamide porous film of the present invention contains aromatic polyamide, and when measuring the range of S μm ² using an atomic force microscope on at least one surface, the cross-sectional area S(10) μm ² at a depth of 10 nm from the surface and the distance from the surface The cross-sectional area S(20) μm ² at a depth of 20 nm simultaneously satisfies the following formula.

0.01≤S(10)/S≤0.3

5≤S(20)/S(10)≤20

Here, the cross-sectional area specified in the present invention means the sum of the areas where the polymer-containing solid content exists when the porous aromatic polyamide film of the present invention is cut horizontally at a certain point in the thickness direction. Therefore, S(10)/S represents the ratio of the solid content of the polymer containing the aromatic polyamide of the present invention at a depth of 10 nm from the surface when the range of S ^μm is measured using an atomic force microscope; S(20)/S (10) represents the ratio of S(20)/S to the above-mentioned S(10)/S, and S(20)/S is when the range of Sμm ² is measured using an atomic force microscope at a depth of 20 nm from the surface, and contains the fragrance of the present invention The ratio of the solid content of the polyamide polymer.

By making S(10)/S≤0.3, when the porous film of the present invention is used as a battery separator, if the surface is arranged on the positive electrode side, the contact area with the positive electrode can be reduced, and the It is preferable that the surface of the aromatic polyamide porous film is oxidized by the active material of the positive electrode. In addition, by forming an appropriate gap between the positive electrode or the negative electrode and the separator, ions are easily moved along the surface direction, and metal lithium is precipitated, so that even if some pores are blocked, it is possible to transfer from other pores to the opposite electrode. It is preferable because the ion permeability is hardly lowered by movement. However, if S(10)/S is less than 0.01, the strength in the thickness direction becomes insufficient, and if the positive and negative electrodes are wound in a spiral shape when processed into a battery, they will be compressed, and the contact area with the positive electrode may increase. . From the viewpoint of achieving both the effect of reducing the contact area with the positive electrode and the strength in the thickness direction in a more balanced manner, 0.02≤S(10)/S≤0.2 is more preferred, and 0.03≤S(10)/S≤0.15 is further preferred.

In addition, if S(20)/S(10) is less than 5, the strength in the plane direction becomes insufficient and may be broken during the processing process. If S(20)/S(10) exceeds 20, ions may permeate Sexual inadequacy. When S(20)/S(10) is 5 to 20, the strength in the plane direction and the ion permeability can be well balanced, and from the viewpoint of better balancing these properties, 5 is more preferable. ≤S(20)/S(10)≤15, more preferably 5≤S(20)/S(10)≤10.

S(10) μm ² and S(20) μm ² were measured using an atomic force microscope (AFM) under the following conditions.

Device: NanoScope III AFM (manufactured by Digital Instruments)

Cantilever: Silicon single crystal

Scan mode: tap mode

Scanning range: 30μm×30μm

Scan speed: 0.5Hz

Measurement environment: 25°C, relative humidity 65%

Processing software: NanoScope III ver.3.12

Calculate the cross-sectional area at every 5nm along the height direction from the reference plane, take the part where the cross-sectional area initially becomes 0 as the surface, record the cross-sectional area cut at a depth of 10nm from the surface as S(10)μm ² , and The cross-sectional area cut at a depth of 20 nm is recorded as S(20) μm ² for calculation.

The aromatic polyamide porous film of the present invention preferably has a Gurley value of 5 to 500 sec/100 cc. In the aromatic polyamide porous film of the present invention, if the Gurley value is within the above range, the strength in the plane direction can be maintained even in a region where the Gurley value is small. Appropriate porosity and pore diameter can also be imparted to a region with a large value. If the Gurley value is less than 5 sec/100 cc, the strength in the plane direction is remarkably low, and if the Gurley value is greater than 500 sec/100 cc, the ion permeability may be insufficient. The Gurley value is more preferably 10 to 300 sec/100 cc, and the Gurley value is still more preferably 30 to 200 sec/100 cc, from the viewpoint of achieving both strength in the plane direction and ion permeability in a more balanced manner.

In addition, if the aromatic polyamide porous film of the present invention has a three-dimensional network structure, the ion conductivity is good, and even in the case of metal lithium precipitation, because the path connecting the positive electrode and the negative electrode is very long, it becomes It is complicated, so it is difficult to produce a short circuit between the positive electrode and the negative electrode, that is, a short, so it is preferable. The three-dimensional network structure mentioned in the present invention means, for example, as shown in FIG. 1 , that the solid content (fibrous material) containing the aromatic polyamide polymer constituting the porous film has three or more branches. A structure in which the network structure of the intersection points expands three-dimensionally. In addition, the three-dimensional network structure has pores divided by the solid component containing the aromatic polyamide polymer forming the network. On the other hand, an aromatic polyamide porous film having a structure of straight holes (see FIG. 2 ) and an aromatic polyamide porous film having a structure of straight holes bent or branched through holes (see FIG. 3 ), It is not preferable from the point of view of easy short-circuit in the case of metal lithium precipitation, and the aromatic polyamide porous film with a structure in which spherical or disc-shaped pores are connected by very fine channels (see FIG. 4 ), from the ion conduction From the viewpoint of low performance, it is not preferable. In addition, such a porous aromatic polyamide film does not satisfy 0.01≤S(10)/S≤0.3, 5≤S(20)/S(10)≤20.

The porous aromatic polyamide film of the present invention preferably has a heat shrinkage rate of 2% or less at 200° C. in at least one direction. If it is more than 2%, if it is used at a high temperature, the shrinkage of the separator may cause a short circuit, the pores may be destroyed, and the ion conductivity may be lowered. In addition, the lower limit is 0%. From the viewpoint of higher heat resistance, the heat shrinkage rate at 200° C. is more preferably 1.5% or less, and still more preferably 1% or less.

The aromatic polyamide film of the present invention preferably has a Young's modulus of 3 GPa or more in at least one direction and an elongation of 5% or more. By making Young's modulus and elongation high, high tension and tension fluctuations during processing can be resisted, and productivity can be improved. In order to satisfy these characteristics, as described above, it is effective that the aromatic rings of the aromatic polyamide used in the present invention have a para-orientation portion, preferably accounting for 80 mol% or more of all aromatic rings, more preferably 90 mol%. above (productivity becomes good). More preferably, the Young's modulus in at least one direction is 4.5 GPa or more, and the elongation is 10% or more. Considering the general characteristics of aromatic polyamides, the upper limit of Young's modulus is 15 GPa, and the upper limit of elongation is about 60%.

The aromatic polyamide porous film of the present invention preferably has a thickness of 2 to 20 μm. When the thickness exceeds 20 μm, the capacity per battery may not be sufficient, and when the thickness is less than 2 μm, the strength may not be sufficient.

Next, the method for producing the aromatic polyamide porous film of the present invention will be described below, but not limited thereto.

First, in the case of obtaining aromatic polyamides such as acid chlorides and diamines, passing a solution in an aprotic organic polar solvent such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, etc. The method of synthesizing by polymerization; the method of synthesizing by interfacial polymerization at the interface of an aqueous layer and an organic solvent layer such as carbon tetrachloride or hexane. If acid chlorides and diamines are used as monomers, hydrogen chloride is by-produced in the polymer solution, and in the case of neutralizing it, inorganic neutralizing agents such as calcium hydroxide, calcium carbonate, lithium carbonate, and epoxy resin can be used. Organic neutralizers for ethane, propylene oxide, ammonia, triethylamine, triethanolamine, diethanolamine, etc. In addition, when an aromatic polyamide is obtained by reacting an isocyanate and a carboxylic acid, it can be synthesized in the above-mentioned aprotic organic polar solvent in the presence of a catalyst such as pyridine or triethylamine.

In order to obtain the porous film of the present invention, the intrinsic viscosity ηinh of the polymer synthesized as above (the value measured at 30° C. of 100 ml of a 0.5 g polymer in 98% by weight sulfuric acid) is preferably 0.5 (dl/g ) above, because this makes the elongation increase and the bonding property become good when forming a porous film.

In the film-forming stock solution containing the aromatic polyamide obtained by interfacial polymerization at the interface of the above-mentioned organic solvent layer and the organic solvent, or in the film-forming stock solution containing the aromatic polyamide synthesized in the above-mentioned aprotic organic polar solvent and the In the film-forming stock solution of organic polar solvents, inorganic salts, such as potassium chloride, magnesium chloride, lithium chloride, lithium nitrate, etc., are sometimes added as auxiliary solvents. As a membrane-forming stock solution, in order to adjust the solubility of the polymer, a poor solvent for the polymer represented by alcohols such as water, acetone, methanol, and ethanol may be added to the neutralized polymer (aromatic polyamide) solution, Alternatively, water-soluble polymers represented by polyvinyl alcohol, polyvinylpyrrolidone, and polyethylene glycol may be added and used. In addition, the poor solvent of a polymer mentioned here means the solvent which cannot dissolve 1 g or more of polymers in 100 ml of solvents at 25 degreeC.

In addition, as the film-forming stock solution, a solution in which the polymer is separated and then dissolved in the above-mentioned aprotic organic polar solvent, and the above-mentioned poor solvent and the water-soluble polymer are mixed can be used. The concentration of the polymer in the membrane-forming stock solution is preferably about 2 to 30% by weight. In order to efficiently obtain a thin and stable porous film, it is preferably 2 to 30% by weight, more preferably 8 to 25% by weight, and even more preferably 12 to 20% by weight. In addition, in order to precipitate the polymer quickly, it is preferable to mix the poor solvent and the water-soluble polymer in an amount of 2 to 40% by weight. More preferably, it is 5 to 30 weight%, More preferably, it is 10 to 25 weight%.

The membrane-forming stock solution prepared as above can be formed into a porous thin film by a so-called solution membrane-forming method. The solution membrane-forming method includes a dry-wet method, a wet method, and a precipitation method, and any method may be used to form a membrane, but the precipitation method is more preferable in order to obtain a membrane with a uniform internal structure of a porous thin film.

In the case of producing a porous film by the precipitation method, the film-forming stock solution is cast onto a support such as a glass plate, film, roller, or endless belt to form a film. Next, the solubility of the polymer is lowered and precipitated by cooling and absorbing water. In this case, from the viewpoint of easy control of the deposition rate, a method of cooling the film-forming stock solution after forming it into a film shape is more preferable.

In the method of cooling the film-forming stock solution into a film shape, the temperature of the support and the ambient temperature around the support on which the film-forming stock solution is cast are set to -30 to 0°C. When the temperature is lower than -30°C, precipitation is rapid, and S(10) and S(20) may not satisfy the range of the present invention, and the entire system may freeze, and through holes may not be formed. In addition, when the temperature exceeds 0° C., the solubility of the polymer cannot be sufficiently lowered, and the polymer does not precipitate, so that through holes may not be formed. The temperature of the support body and the ambient temperature around the support body of the film-casting stock solution are more preferably -20 to -5°C, because the pore structure of the present invention can be formed in a relatively short time. Furthermore, it is preferable to reduce the difference in physical properties between the surface and the back of the film by setting the absolute value of the difference between the temperature of the support and the ambient temperature around the support of the casting dope within 15°C.

The cooling time of the film-forming stock solution is preferably 1 to 20 minutes. Here, the cooling time of the film-forming stock solution means the time from immediately after casting the film-forming stock solution to introducing it into a wet bath. If the time is less than 1 minute, the formation of pores may be insufficient, and the Gurley value may increase, that is, the ion permeability may deteriorate. If it exceeds 20 minutes, the pores may become too large and the film may become brittle, making it impractical for practical use.

More preferably, before casting the film-forming stock solution on the support, the polymer solution is temporarily cooled to -15 to 15°C with a die and piping, so that the temperature of the support is the same as that around the support where the film-forming stock solution is cast. The absolute value of the atmosphere temperature difference is within 15°C. When cooling in a state where the absolute value of the temperature difference exceeds 15° C., S(10) and S(20) may not satisfy the scope of the present invention.

In addition, in the method of making the film-forming stock solution into a film shape and then absorbing water, any method of adhering mist water, introducing it into water, or introducing it into humidity-controlled air may be used. However, it is preferable to use the method of introducing the water into the humidity-conditioned air in view of the ability to precisely control the absorption rate and amount of water. When the polymer solution formed into a film shape is introduced into humidity-controlled air, it is preferable to precipitate the polymer contained in the film-forming stock solution in air adjusted to a relative humidity of 50 to 100%. The temperature of the humidity-conditioned air at this time is preferably 0 to 80°C.

The solution in which the precipitation of the polymer is completed is then introduced into a wet bath for desolvation. At this time, it may be peeled from the support and introduced into a wet bath, or may be peeled after being introduced into a wet bath together with the support. The bath composition is not particularly limited as long as the solubility of the aromatic polyamide in the bath is low, but it is preferable to use water, N-methylpyrrolidone, or dimethylacetamide from the viewpoint of economy and ease of handling. Mixed system of organic solvents and water. In addition, inorganic salts such as lithium chloride, lithium bromide, and calcium carbonate may be contained in the wet bath. At this time, in the case of adopting a method of cooling the film-forming stock solution into a film shape, it is preferable to set the difference (Ta-Tb) between the temperature (Ta) of the wet bath and the film temperature (Tb) before introduction of the wet bath to be 0～10℃. When the temperature is less than 0°C, the desolvation rate may decrease and the productivity may decrease significantly, and if it exceeds 10°C, S(10) and S(20) may not satisfy the scope of the present invention. In particular, when cooling to a low temperature of less than -10°C, it is preferable to introduce the film into a wet bath after once raising the film temperature to 0°C. In addition, when the film temperature is temporarily raised to 0°C and then introduced into a wet bath, the cooling time of the film-forming stock solution in the present invention means that it starts immediately after the film-forming stock solution is cast until the film temperature reaches 0°C. time so far.

Heat treatment is performed on the porous thin film after desolvation has been completed. The heat treatment temperature at this time is preferably performed at a higher temperature in order to improve the dimensional stability at high temperature, but it must be performed at or below the thermal decomposition temperature of the polymer used. In order to thermally decompose the aromatic polyamide at 350 to 400°C, it is preferable to perform heat treatment at a temperature lower than this, that is, 250 to 320°C. At this point, stretching can be performed. The stretch ratio is preferably 1.0 to 4.0 times in terms of area ratio from the viewpoint of controlling Young's modulus and elongation within the preferred ranges of the present invention, and more preferably during heat treatment in order to further increase the elongation. , In the extent that the film does not shrink, it is 1.0 to 1.1 times.

The aromatic polyamide porous film of the present invention can be suitably used for filters, separation membranes, separators for batteries, printed circuit boards, and the like. Among them, it is preferable to manufacture a secondary battery by using it as a battery separator, and it is particularly preferable to manufacture a lithium ion secondary battery.

As the lithium ion secondary battery, it is preferable to use carbon materials such as graphite and amorphous hard carbon for the negative electrode, and lithium cobalt oxide (composition formula LiCoO ₂ ) with a layered structure and lithium cobalt oxide with a spinel structure for the positive electrode. Lithium transition metal oxide represented by manganese oxide (composition formula LiMn ₂ O ₄ ), as an electrolyte, in an organic solvent or the organic solvent and lithium salt, especially ethylene carbonate and propylene carbonate commonly used at present Trimethyl phosphate, triethyl phosphate, tripropyl phosphate, etc. are mixed and used. In addition, by interposing the aromatic polyamide porous film of the present invention as a battery separator between the positive electrode and the negative electrode, it is possible to prevent a short circuit caused by contact between the active materials of the two electrodes, retain the electrolyte solution, and ensure good conductivity.

In addition, when the lithium ion secondary battery is placed in the engine compartment of a vehicle such as a hybrid vehicle or a fuel cell vehicle that runs at a high temperature, the high positive electrode oxidation resistance and high output characteristics can be fully exhibited.

[Example]

[Measurement method of physical properties and evaluation method of effect]

The measurement methods of the physical properties and the evaluation methods of the effects in the examples were carried out according to the following methods. (1) S(10)μm ² and S(20)μm ²

Using an atomic force microscope (AFM), it measured under the following conditions. The measurement points were five points at intervals of 10 cm along the longitudinal direction (film-forming direction) at the central portion in the film width direction, and the average value was obtained. Calculate the cross-sectional area every 5nm along the height direction from the reference value, record the surface when the cross-sectional area initially reaches 0, record the cross-sectional area cut at a depth of 10nm from the surface as S(10)μm ² , and record the cross-sectional area at a depth of 20nm from the surface as S(10)μm 2 The cut cross-sectional area is recorded as S(20) μm ² for calculation.

Device: Nano Scope III AFM (manufactured by Digital Instruments)

Cantilever: Silicon single crystal

Scan mode: tap mode

Scanning range: 30μm×30μm

Scan speed: 0.5Hz

Measurement environment: 25°C, relative humidity 65%

Processing software: NanoScope III ver.3.12

(2) 3D mesh structure

Using an ultra-high resolution field emission type scanning electron microscope (SEM) S-900H manufactured by Hitachi, Ltd., under the following conditions, observe the central part of the surface of the porous film, and 5 parts of the upper, lower, left, and right sides of the central part. Undergo verification.

Acceleration voltage: 5kV

Observation magnification: 30000 times

(3) Gurley value

According to the method stipulated in JIS-P8117 (1998), the widthwise central portion of the porous film and five portions of the portion 5 cm above, below, left, and right from the central portion were measured, and an average value was obtained. The porous film of the sample was tied to a circular hole with a diameter of 28.6 cm and an area of 645 mm ² . Let the air in the cylinder pass through the inner cylinder (inner cylinder weight 567g) from the test hole to the outside of the cylinder. The time for passing 100 cc of air is measured as the Gurley value. As a measuring device, a B-type Gurley air permeability meter (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) was used.

(4) Heat shrinkage rate

The porous film was cut into a rectangle having a width of 1 cm and a length of 22 cm, with the long side being the measurement direction. Mark the part 1 cm from both ends of the long side, heat-treat for 30 minutes in a hot air oven at 200° C. in a state where tension is not applied substantially, then measure the distance between the marks, and calculate according to the following formula. The measurement was performed five times each in the longitudinal direction and the width direction of the film, and the average value was obtained.

Thermal shrinkage rate (%)=((interval before heat treatment-interval after heat treatment and cooling)/interval before heat treatment)×100.

(5) Young's modulus and elongation

The measurement was carried out at 23° C. and a relative humidity of 65% using Robot Tension RTA (manufactured by Orientec Corporation). The test piece was cut out so that it may form the rectangle of 10 mm in width and 100 mm in length, and the long side shall be a measurement direction. The stretching speed was 300 mm/min. The measurement was performed five times each in the longitudinal direction and the width direction of the film, and the average value was obtained.

(6) Thickness

Using an electronic micrometer manufactured by Kansai Anritsu Electronics Co., Ltd. (detector model K107C, stylus radius 1.5mm, stylus load 1.5g), in the center of the width direction, at 5 places up, down, left, and right based on the center in the width direction The measurement was performed, and the average value was obtained.

(7) Battery characteristics

A. Modulation of electrolyte

Dissolve LiC ₄ F ₉ SO ₃ in trimethyl phosphate, then add propylene carbonate for mixing, and prepare 0.6 moles of /L LiC ₄ F ₉ SO ₃ organic electrolyte. In order to examine the ignition point of the organic electrolytic solution obtained in this way, the electrolytic solution was heated to a predetermined temperature, and the flame was brought close to the vicinity of the liquid surface to examine whether or not it ignites. No ignition occurred in the tests at 100°C, 150°C, and 200°C, and it can be seen that the ignition point of this electrolytic solution is 200°C or higher.

B. Production of batteries

Graphite and polyvinylidene fluoride are added to lithium cobalt oxide (LiCoO ₂ ), and the slurry dispersed in a solvent is uniformly coated on both sides of an aluminum foil for a positive electrode current collector with a thickness of 10 μm, dried, and compressed Molded to produce a strip-shaped positive electrode. The thickness of the positive electrode was 40 μm.

Coke and polyvinylidene fluoride as a binder are mixed to form a negative electrode mixture, which is dispersed with a solvent to form a slurry. The negative electrode mixture slurry was used as a negative electrode current collector, and was evenly coated on both sides of a strip-shaped copper foil with a thickness of 10 μm, dried, and compression-molded to prepare a strip-shaped negative electrode precursor. As a treatment liquid for the negative electrode precursor, LiC ₄ F ₉ SO ₃ was dissolved in trimethyl phosphate, and then ethylene carbonate was added and mixed to prepare a treatment liquid. The Li foil (foil) with the lead body pressed on it is clamped on both sides of the negative electrode precursor through the separator immersed in the treatment solution, and added to the container (holder), and the negative electrode precursor is used as the positive electrode and the Li electrode is used as the negative electrode. Discharge and Charge. Then, it was decomposed in the container, and the negative electrode precursor was washed with dimethyl carbonate and dried to prepare the negative electrode. The thickness of the negative electrode was 50 μm.

Next, pass the above-mentioned strip-shaped positive electrode through the diaphragm film of each embodiment, overlap with the above-mentioned foil-shaped negative electrode, and roll it into a spiral shape to form a spiral electrode body, and then fill it into a bottomed cylindrical battery case with an inner diameter of 13 mm. After the positive and negative electrodes are welded with lead body, the organic electrolyte is injected into the battery case. The opening of the battery case was sealed, and the battery was precharged to produce a cylindrical organic electrolyte secondary battery. Ten secondary batteries were produced, and the following evaluations were performed.

C. Battery Characteristics

Each secondary battery produced was charged at 4.1 V and discharged at 2.7 V at 35 mA in an atmosphere of 150° C., and the discharge capacities of the first cycle and the 100th cycle were examined.

Regarding (1) (2), the average value of 10 secondary batteries was calculated|required. In addition, regarding (2), the calculation was performed except for a battery that ruptured or caught fire during the charging and discharging operation.

(1) Initial characteristics

Discharge capacity in the first cycle (mA·h/g)

(2) Cycle characteristics

Based on the discharge capacity at the first cycle, the discharge capacity at the 100th cycle was evaluated according to the following criteria. Above B is the practical range.

A: More than 95%

B: More than 90% and less than 95%

C: Less than 90%

(3) The number of bad

The number of battery ruptures and fires during the charging and discharging operations up to the above-mentioned 100 cycles was examined.

Hereinafter, the present invention will be described more specifically based on examples, but it cannot be said that the present invention is limited to these examples.

(Example 1)

In dehydrated N-methyl-2-pyrrolidone, dissolve 80 mol % of 2-chloro-p-phenylenediamine relative to the total amount of diamines and 20 mol % of 4,4'- Diaminodiphenyl ether, 2-chloroterephthaloyl chloride of 98.5 mol% relative to the total amount of diamine was added thereto, and after stirring for 2 hours, polymerization was carried out, and then neutralized with lithium carbonate to obtain a polymer concentration It is an 11% by weight aromatic polyamide solution. This solution was put into a mixer together with water, and the polymer was precipitated and taken out while stirring.

Weigh such that the polymer is 10% by weight, N-methyl-2-pyrrolidone is 70% by weight, and polyethylene glycol (average molecular weight: 200) is 20% by weight, and the polymer is dissolved in N at 60°C. - After adding to methyl-2-pyrrolidone, polyethylene glycol was added to obtain a homogeneous and completely miscible polymer solution.

This polymer solution was supplied to a die, and cast onto a stainless steel belt to form a film of about 100 μm. The temperature of the die and the piping leading to the die was set at 5°C, and the temperature of the belt and the atmosphere around the belt was set at -5°C. The cast polymer solution was cooled on a belt for 5 minutes to precipitate and form a porous film. This porous film was peeled off from the tape, and the extraction of the solvent and the impurities was performed in a water bath at 5° C. for 2 minutes and then in a water bath at 50° C. for 1 minute. Then, while stretching to 1.1 times in the width direction in a tenter, heat treatment was performed at 320° C. for 2 minutes to obtain a porous aromatic polyamide film.

The main production conditions are shown in Table 1, and the physical properties of the obtained porous film are shown in Table 2. The initial capacity, cycle characteristics, and defect rate were all good. In addition, observation with SEM confirmed that a three-dimensional network structure was formed.

(Example 2)

A porous film was obtained in the same manner as in Example 1 except that the polymer solution obtained in the same manner as in Example 1 was used, except that the film thickness during casting was about 50 μm, and the cooling time was 20 minutes. The initial capacity, cycle characteristics, and defect rate were all good.

(Example 3)

A porous film was obtained in the same manner as in Example 1 except that the polymer solution obtained in the same manner as in Example 1 was used, except that the temperature of the belt and the ambient temperature around the belt were 0°C. Both the initial capacity and cycle characteristics were lower than in Example 1, but within the practical range.

(Example 4)

Using the precipitation polymer obtained by the same operation as in Example 1, the polymer is 10% by weight, and N-methyl-2-pyrrolidone is 90% by weight (without adding polyethylene glycol), to make a membrane-forming solution, and to make the film-forming solution with A porous film was obtained in the same manner as in Example 1, except that the temperature and the ambient temperature around the belt were -10°C, and the cooling time was 10 minutes. Both the initial capacity and cycle characteristics were lower than in Example 1, but within the practical range.

(Example 5)

In Example 1, the addition amount of the monomer is such that the addition amount of 2-chloro-p-phenylenediamine is 50 mole % relative to the total amount of diamines, and the addition of 4,4'-diaminodiphenyl ether A porous film was obtained in the same manner as in Example 1, except that the amount was 50 mol % with respect to the total amount of diamine. The Young's modulus is very low, the filling rate is low, and the initial capacity is lower than that of Example 1, but it is within the practical range. The cycle characteristics were also lower than in Example 1, but within the practical range.

(Example 6)

Using the precipitation polymer obtained by the same operation as in Example 1, the polymer is 10% by weight, N-methyl-2-pyrrolidone is 80% by weight, and polyethylene glycol (average molecular weight 200) is 10% by weight to prepare For the film forming solution, the support body is a PET film with a thickness of 100 μm, the thickness during casting is 25 μm, the temperature of the die and the piping to the die is -15°C, the temperature of the PET film and the ambient temperature around the PET film are A porous film was obtained in the same manner as in Example 1 except that the temperature was -30°C and the cooling time was 20 minutes. Here, the cooled polymer solution was once heated to 0° C. and then introduced into a water tank. The initial capacity, cycle characteristics, and defect rate were all excellent.

(Example 7)

In Example 1, a porous film was obtained in the same manner as in Example 1 except that the thickness at the time of casting was 8 μm. The initial capacity is large, and on the other hand, the number of defects increases, but it is within the practical range.

(Embodiment 8)

In Example 1, except that the thickness at the time of casting was 200 μm, a porous film was obtained in the same manner as in Example 1. The initial capacity was small, and the cycle characteristics were also lower than in Example 1, but within the practical range.

(Example 9)

Using the film-making solution of Example 1, cast it on the PET film with a thickness of 100 μm, and make the thickness be 150 μm, and treat it in an atmosphere of 90% relative humidity at 15° C. for 30 minutes, after the water tank, use the same method as in Example 1 Porous films were obtained by the same method. There are a lot of bad ones, but they are within the practical range.

(Example 10)

Using the film-forming solution of Example 1, casting on a PET film with a thickness of 100 μm, and making the thickness 120 μm, each PET film was introduced into a bath of NMP/water=80/20% by volume at 5° C. for 5 minutes, After the water tank, a porous film was obtained in the same manner as in Example 1. The cycle characteristic was low and the number of defects was high, but it was within the practical range.

(comparative example 1)

In Example 1, except that the cooling time was 0.5 minutes, a porous film was obtained in the same manner as in Example 1. The initial capacity and cycle characteristics are poor.

(comparative example 2)

In Example 1, a porous film was obtained in the same manner as in Example 1, except that the die temperature was 10°C, and the belt and the ambient temperature around the belt were -10°C. The initial capacity and cycle characteristics were poor.

(comparative example 3)

In Example 1, a porous film was obtained in the same manner as in Example 1, except that the die temperature was 10°C, the atmosphere temperature of the belt and its surroundings was -10°C, and the bath temperature was 10°C. The initial capacity and cycle characteristics were poor.

(comparative example 4)

In Example 1, except that the cooling time was 30 minutes, a porous film was obtained in the same manner as in Example 1. The cycle characteristics and defect rate were poor.

(comparative example 5)

In Example 1, a porous film was obtained in the same manner as in Example 1, except that the die temperature was 5°C, and the belt and the ambient temperature around the belt were -40°C. The Gurley value was large, (low ionic conductivity), so battery characteristics could not be evaluated.

(comparative example 6)

Using the polymer solution obtained in the same manner as in Example 1, it was cast onto a PET film with a thickness of 100 μm to a thickness of 100 μm, and each PET film was introduced into a water bath at 5° C. for 5 minutes. Next, extraction of the solvent and impurities was performed in a water tank at 50° C. for 1 minute. Then, it was stretched to 1.1 times in the width direction in a tenter and heat-treated at 320° C. for 2 minutes to obtain a porous aromatic polyamide film. When observed by SEM, no pores were formed at all. Therefore, battery characteristics could not be evaluated.

(comparative example 7)

Using the precipitation polymer obtained in the same manner as in Example 1, the polymer was 10% by weight and N-methyl-2-pyrrolidone was 90% by weight (without adding polyethylene glycol) to prepare a film-forming solution. This solution was cast onto an endless belt so as to have a thickness of about 130 μm, heated with hot air at 180° C. for 2 minutes to evaporate the solvent, and the self-retaining film was continuously peeled from the belt. Next, the thin film was introduced into a water tank at 50° C., and the inorganic salt produced by neutralizing the remaining solvent was extracted with water. Then, after pre-drying at 80° C. for 30 seconds with a tenter, stretching to 1.1 times in the transverse direction while heat-treating at 280° C. for 1.5 minutes, an aramid film having a thickness of 12 μm was obtained.

The film was passed under pressure between an iron roll plated with a plurality of synthetic diamond particles with a particle size of 50 to 60 μm and sharp corners on the surface and a polysiloxane rubber roll to obtain an aromatic polyamide. Amide porous film.

From the observation of SEM, it turns out that a straight hole was formed. Cycle characteristics are poor.

(comparative example 8)

Using the precipitation polymer obtained in the same manner as in Example 1, the polymer was 10% by weight and N-methyl-2-pyrrolidone was 90% by weight (without adding polyethylene glycol) to prepare a film-forming solution. Surfactant ("Homogenol" L-18 manufactured by Kao) and zinc oxide microparticles with an average particle diameter of 1 μm (manufactured by High Purity Chemical Co., Ltd., specific gravity 5.47) were respectively 2% by weight and 80% by weight with respect to the polymer, in a nitrogen atmosphere. Heating to 60°C under flow, while uniformly dispersing and mixing into the above solution. Next, an aromatic polyamide film having a thickness of 12 μm was obtained in the same manner as in Comparative Example 7.

This film was dipped in a 5% nitric acid aqueous solution for 30 minutes to dissolve and remove fine zinc oxide particles dispersed in the white film. Then, after washing in a water tank at 40° C., drying treatment was performed at 100° C. for 1 minute to obtain a porous aromatic polyamide film. The cycle characteristics and defect rate were poor.

industrial availability

The present invention is an aromatic polyamide porous film that can be suitably used as a filter, a separation membrane, a battery separator, a printed circuit board, etc., especially a battery separator that can be used at high temperatures for a long period of time.

Claims (10)

1. an aromatic polyamide porous film contains aromatic polyamide, at least one side's surface, uses atomic force microscope to measure S μ m ²Scope the time, apart from sectional area S (10) the μ m at surperficial 10nm degree of depth place ²With sectional area S (20) μ m apart from surperficial 20nm degree of depth place ²Satisfy following formula simultaneously,

0.01≤S(10)/S≤0.3

5≤S(20)/S(10)≤20

Aromatic polyamide forms 3 dimension reticulated structures.

2. aromatic polyamide porous film as claimed in claim 1, Ge Erlai value are 5～500 seconds/100cc.

3. aromatic polyamide porous film as claimed in claim 1, at least one direction is below 2% at 200 ℃ percent thermal shrinkage.

4. aromatic polyamide porous film as claimed in claim 1, the young's modulus in tension of at least one direction are more than the 3GPa and elongation is more than 5%.

5. aromatic polyamide porous film as claimed in claim 1, thickness are 2～20 μ m.

6. aromatic polyamide porous film as claimed in claim 1 is used as battery separator.

7. a secondary cell is to use the described aromatic polyamide porous film of claim 1 to form.

8. the manufacture method of an aromatic polyamide porous film, it is manufacture method with aromatic polyamide porous film of following operation, described operation is: in the system pleurodiaphragmatic in terspace liquid curtain coating that will contain aromatic polyamide and organic solvent to support, form the operation of membranoid substance, with above-mentioned membranoid substance refrigerative operation, cooled membranoid substance is imported to the operation that wet type is bathed, wherein, atmosphere temperature around the support of support temperature or casting film stoste is cooled to-30～0 ℃, making the cooling time of system pleurodiaphragmatic in terspace liquid is 1～20 minute, and the temperature head of the temperature T b of the membranoid substance before making the temperature T a of wet type bath and importing to the wet type bath is that Ta-Tb is 0～10 ℃.

9. the manufacture method of aromatic polyamide porous film as claimed in claim 8, the absolute value of temperature head that makes the atmosphere temperature around the support of support temperature and casting film stoste is in 15 ℃.

10. the manufacture method of aromatic polyamide porous film as claimed in claim 8 is in the system pleurodiaphragmatic in terspace liquid before system pleurodiaphragmatic in terspace liquid curtain coating is to the support, add the poor solvent or the water-soluble polymers of the polymkeric substance in the system pleurodiaphragmatic in terspace liquid.

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